The present invention relates to a gas replacement method and, more particularly, to a method of replacing atmospheric gas in the optical path of vacuum ultraviolet light from outer air to inert gas in a semiconductor exposure apparatus using vacuum ultraviolet light as a light source, and an exposure apparatus for performing this gas replacement.
Along with the trend toward increasing the integration degree and micropatterning semiconductor devices, demands have arisen for higher resolution in exposure apparatuses such as a stepper. The resolution is proportional to the wavelength of exposure light. The exposure wavelength is becoming shorter, and a g-line (wavelength: 436 nm) in the visible region changes to an i-line (wavelength: 365 nm) in the ultraviolet region. Recently, a KrF excimer laser beam (wavelength: 248 nm) is used, and the use of an ArF excimer laser beam (wavelength: 193 nm), an F2 laser beam (wavelength: 157 nm), and an Ar2 laser beam (wavelength: 126 nm) has been examined.
In a wavelength region of the ArF excimer laser beam or shorter, absorption by oxygen in air occurs, and the transmittance decreases. To prevent this, an exposure apparatus using an ArF excimer laser beam replaces most of gas in the optical path of exposure light by nitrogen. Even nitrogen causes slight absorption in a wavelength region of 190 nm or less (vacuum ultraviolet light), so nitrogen must be replaced by another gas (inert gas other than nitrogen) which transmits light. The atmosphere around the optical path of exposure light and an optical element is most desirably replaced by helium in consideration of high safety, high thermal conductivity, and small changes in refractive index by the temperature in such gas.
In general, to replace outer air in the optical path of exposure light by another gas, the optical path is incorporated in a closed vessel, replacement gas is supplied from a supply port by using one end of the closed vessel as the gas supply port and the other end as a discharge port, and a gas flow path is formed in the closed vessel so as to fill the entire optical path with the replacement gas. Gas in the closed vessel is replaced by convection and molecular diffusion.
Gas supplied to the closed vessel purges the outer air present in the vessel from the beginning. On this stage, the concentration around the discharge port hardly changes. Then, convection discharges the diluted outer air. On this stage, the concentration of the original outer air exponentially rapidly decreases. After that, the concentration gradually decreases. This is considered that gas replacement at a stagnation point at which gas hardly flows is progressed by molecular diffusion.
Only when gas replacement at a stagnation point at which gas hardly flows is progressed by molecular diffusion, does it take a very long time to decrease the concentration of gas present in the vessel from the beginning.
On the other hand, a continuous absorption band by oxygen exists in the wavelength region of vacuum ultraviolet light. Light is greatly absorbed at a high oxygen concentration in the optical path, and the oxygen concentration must be suppressed to about 1 ppm or less in the use of an exposure apparatus. If, however, air is replaced by helium by the conventional method, gas replacement at a stagnation point is mainly performed by only molecular diffusion, and it takes a long time to replace gas to a desired oxygen concentration.
The present invention has been proposed to solve the conventional problems, and has as its object to rapidly purge outer air in a vessel which airtightly contains the periphery of the optical path of exposure light for a semiconductor exposure apparatus.
An exposure apparatus of the present invention for achieving the above object comprises a chamber which incorporates an optical element and surrounds a predetermined region, a closed vessel which surrounds the chamber, and a pump for reducing an internal pressure of the chamber, wherein a pressure of the closed vessel is also reduced when the internal pressure of the chamber is reduced.
The chamber is desirably supported by the closed vessel.
The exposure apparatus desirably further comprises a displacement mechanism for generating a displacement between the chamber and the closed vessel.
The exposure apparatus desirably further comprises a measurement device for measuring a positional relationship between a reference member and the chamber. It is preferable that a positional relationship between a reference member and the chamber be measured and that a displacement mechanism be controlled based on a measurement result.
The closed vessel desirably has a transmission window for transmitting light, and the transmission window is preferably formed from fluoride glass.
The closed vessel desirably has an opening/closing door.
The exposure apparatus desirably further comprises a vent hole for allowing the chamber and the closed vessel to communicate with each other, and the vent hole is preferably freely opened/closed.
The pump desirably discharges gas from the closed vessel.
The pump desirably discharges gas from the closed vessel to discharge gas from the chamber via a vent hole formed in the chamber.
The pump desirably discharges gas from the chamber.
The chamber desirably incorporates at least some of the optical elements of an illumination optical unit.
The chamber desirably incorporates at least some of the optical elements of a projection optical unit.
Inert gas is desirably supplied after the internal pressure of the chamber is reduced. The inert gas preferably includes at least one of helium and nitrogen.
The internal pressure of the chamber is desirably reduced a plurality of number of times.
The chamber desirably has a gas supply port and a gas discharge port.
The chamber desirably surrounds at least part of an optical path of light in a vacuum ultraviolet region.
Another exposure apparatus of the present invention comprises a chamber which incorporates an optical element and surrounds a predetermined region, a mechanism for setting an inert gas atmosphere in the chamber, and a closed vessel which surrounds the chamber, wherein a purity of inert gas in the chamber is higher than a purity of inert gas in the closed vessel.
The purity of the inert gas in the closed vessel is desirably higher than a purity of inert gas outside the closed vessel.
The mechanism desirably discharges gas from the chamber before setting the inert gas atmosphere in the chamber.
The closed vessel desirably has a transmission window for transmitting light, and the transmission window is preferably formed from fluoride glass.
The closed vessel desirably has an opening/closing door. The exposure apparatus desirably further comprises a vent hole for allowing the chamber and the closed vessel to communicate with each other, and the vent hole is preferably freely opened/closed.
The chamber desirably incorporates at least some of the optical elements of an illumination optical unit.
The chamber desirably incorporates at least some of the optical elements of a projection optical unit.
The inert gas desirably contains at least one of helium and nitrogen.
The chamber desirably surrounds at least part of an optical path of light in a vacuum ultraviolet region.
Still another exposure apparatus of the present invention comprises a chamber which incorporates an optical element and surrounds a predetermined region, a mechanism for setting an inert gas atmosphere in the chamber, and a closed vessel which surrounds the chamber, wherein an internal pressure of the chamber is higher than an internal pressure of the closed vessel.
A pressure of inert gas in the closed vessel is desirably higher than a pressure of inert gas outside the closed vessel.
The mechanism desirably discharges gas from the chamber before setting the inert gas atmosphere in the chamber.
The closed vessel desirably has a transmission window for transmitting light, and the transmission window is preferably formed from fluoride glass. The closed vessel desirably has an opening/closing door.
The exposure apparatus desirably further comprises a vent hole for allowing the chamber and the closed vessel to communicate with each other, and the vent hole is preferably freely opened/closed.
The chamber desirably incorporates at least some of the optical elements of an illumination optical unit.
The chamber desirably incorporates at least some of the optical elements of a projection optical unit.
The inert gas desirably includes at least one of helium and nitrogen.
The chamber desirably surrounds at least part of an optical path of light in a vacuum ultraviolet region.
A gas replacement method of the present invention for achieving the above object comprises the steps of reducing an internal pressure of a chamber which incorporates an optical element, reducing a pressure of a closed vessel which surrounds the chamber, and supplying inert gas into the chamber.
Another gas replacement method of the present invention comprises the steps of supplying inert gas into a chamber which incorporates an optical element, supplying inert gas into a closed vessel which surrounds the chamber, and controlling a purity of the inert gas in the chamber to be higher than a purity of the inert gas in the closed vessel.
Still another gas replacement method of the present invention comprises the steps of supplying inert gas into a chamber which incorporates an optical element, supplying inert gas into a closed vessel which surrounds the chamber, and controlling a pressure of the inert gas in the chamber to be higher than a pressure of the inert gas in the closed vessel.
A semiconductor device manufacturing method using any one of the exposure apparatuses also falls within the spirit and scope of the present invention.
A semiconductor manufacturing factory including any one of the exposure apparatuses also falls within the spirit and scope of the present invention.
A maintenance method for any one of the exposure apparatuses also falls within the spirit and scope of the present invention.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.